TECHNICAL FIELD
[0001] The present invention relates to a cathode including a cathode current collector,
a cathode tab protruding from the cathode current collector, and an insulation layer
coated with an insulating material on the cathode tab, and a secondary battery including
the cathode.
BACKGROUND ART
[0002] Demand for secondary batteries as an energy source has been rapidly increased as
technology development and demand with respect to mobile devices have increased, and
as a result, a significant amount of research into batteries that can meet various
demands has been conducted.
[0003] Typically, in terms of the shape of the battery, demand for prismatic type batteries
and pouch type batteries having a thin profile which may be used in products, such
as mobile phones, is high, and, in terms of materials, demand for lithium secondary
batteries, such as lithium cobalt polymer batteries having excellent energy density,
discharge voltage, and safety, is high.
[0004] One of major research projects of these secondary batteries is the improvement of
safety. A leading cause of safety-related incidents in batteries is attributed to
the attainment of an abnormal high-temperature state due to a short circuit between
a cathode and an anode. That is, under normal circumstances, a separator is disposed
between the cathode and the anode to maintain electrical insulation. However, there
may be limitations in using a typical separator alone under abnormal misuse or abuse
conditions, for example, the occurrence of overcharge or overdischarge of the battery,
or dendritic growth of an electrode material or the occurrence of an internal short
circuit due to foreign matter, or the penetration of the battery by sharp objects
such as nails and screws, or excessive deformation of the battery by external force.
[0005] In general, a microporous membrane formed of a polyolefin resin is mainly used as
a separator. However, since the heat resistance temperature thereof is in a range
of about 120°C to about 160°C, heat resistance properties may be insufficient. Therefore,
when the internal short circuit occurs, a state of thermal runaway may be attained
in which the separator shrinks due to short circuit reaction heat to enlarge a short-circuit
part and generate much more reaction heat.
[0006] Also, as illustrated in FIG. 1, a secondary battery is generally prepared in a prismatic
shape by cutting a cathode and an anode in an appropriate size and stacking several
sheets. In this case, since edges of the cathode or the anode that is coated with
a polymer electrolyte may include sharp parts having an inconspicuous tiny needle
shape, a microscopic internal short circuit may occur in these parts when the electrodes
are stacked. Thus, the performance of the battery may be adversely affected. In particular,
since the edges have more irregular surfaces than the inside when coating the polymer
electrolyte, the edges are not evenly coated. Thus, a short circuit is likely to occur.
Also, when upper and lower layers of the electrodes are even slightly misaligned with
each other while stacking the electrodes, a short circuit between the cathode and
the anode may occur.
[0007] Thus, various methods for reducing the possibility of cell deformation, external
impact, or a physical short circuit between the cathode and the anode have been studied.
[0008] For example, in order to prevent the occurrence of a short circuit caused by moving
an electrode assembly in a state in which the battery is completed to allow an electrode
tab to be in contact with an upper end of the electrode assembly, there is a method
of attaching a predetermined sized insulation tape on the electrode tab near an upper
end of a current collector. Typically, a polyimide film is used as the insulation
tape, and it is generally recommend that the insulation tape is wrapped to a slightly
extended length from the upper end of the current collector to the bottom. Also, in
order to prevent loosening, the insulation tape is typically wrapped twice or three
times.
[0009] However, such a winding operation of the insulation tape may be highly complicated,
and in the case that the insulation tape is wrapped to a slightly extended length
from the upper end of the current collector to the bottom, the above wrapped portion
may cause an increase in the thickness of the electrode assembly. Furthermore, the
wrapped portion may be easily loosened during the bending of the electrode tab.
DISCLOSURE OF THE INVENTION
TECHNICAL PROBLEM
[0010] The present invention provides a cathode including a cathode tab which may minimize
the possibility of a physical short circuit between a cathode and an anode due to
cell deformation or shrinkage of a separator in a high-temperature atmosphere, and
a secondary battery including the cathode.
TECHNICAL SOLUTION
[0011] According to an aspect of the present invention, there is provided a cathode including
a cathode current collector; a cathode tab protruding from the cathode current collector;
and an insulation layer coated with an insulating material on the cathode tab.
[0012] According to another aspect of the present invention, there is provided a secondary
battery including the cathode; an anode; and a separator disposed between the cathode
and the anode.
ADVANTAGEOUS EFFECTS
[0013] The present invention may further reduce the possibility of a physical short circuit
between a cathode and an anode due to cell deformation or shrinkage of a separator
in a high-temperature atmosphere by including an insulation layer that is coated with
an insulating material on a cathode tab. In addition, safety and reliability in battery
performance may be significantly improved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The following drawings attached to the specification illustrate preferred examples
of the present invention by example, and serve to enable technical concepts of the
present invention to be further understood together with detailed description of the
invention given below, and therefore the present invention should not be interpreted
only with matters in such drawings.
FIG. 1 illustrates a typical example of the occurrence of a short circuit in a secondary
battery;
FIGS. 2A and 2B are respectively a plan view (2A) and a side sectional view (2B) illustrating
a cathode including a cathode tab which protrudes from a typical cathode current collector;
FIGS. 3A and 3B are respectively a plan view (3A) and a side sectional view (3B) illustrating
a cathode including an insulation layer on a cathode tab that is composed of a non-coating
portion, according to an embodiment of the present invention;
FIGS. 4 to 6 are side sectional views respectively illustrating cathodes including
an insulation layer on a cathode tab including a cathode active material coating portion,
according to an embodiment of the present invention; and
FIG. 7 is a schematic view illustrating a secondary battery including a cathode tab
which includes an insulation layer, according to an embodiment of the present invention.
MODE FOR CARRYING OUT THE INVENTION
[0015] Hereinafter, the present invention will be described in more detail to allow for
a clearer understanding of the present invention.
[0016] It will be understood that words or terms used in the specification and claims shall
not be interpreted as the meaning defined in commonly used dictionaries. It will be
further understood that the words or terms should be interpreted as having a meaning
that is consistent with their meaning in the context of the relevant art and the technical
idea of the invention, based on the principle that an inventor may properly define
the meaning of the words or terms to best explain the invention.
[0017] A cathode according to an embodiment of the present invention may include a cathode
current collector, a cathode tab protruding from the cathode current collector, and
an insulation layer coated with an insulating material on the cathode tab.
[0018] According to an embodiment of the present invention, since the cathode including
the insulation layer on the cathode tab may significantly reduce a preparation process
of a battery, the cathode may eventually reduce preparation costs of the battery and
may further improve the safety of the battery by enlarging an insulation area. In
addition, limitations which may occur when using a typical insulating film or tape,
that is, the possibility of exfoliation during the bending of the cathode tab for
the attachment to the corresponding portion may be very low and an increase in the
thickness of an electrode assembly may not be induced.
[0019] The cathode tab according to an embodiment of the present invention may be formed
in a structure in which at least one side of the cathode tab is coated with an electrically
insulating material (hereinafter, simply referred to as "insulating material").
[0020] According to an embodiment of the present invention, the insulating material may
include any one selected from the group consisting of butyl acrylate, styrene, acrylic
acid, hydroxyethyl acrylate, and a styrene-butadiene rubber (SBR), or a mixture of
two or more thereof. The insulating material may be an aqueous solution in which the
insulating material is dispersed in an amount of 10 wt% to 90 wt% in water.
[0021] According to an embodiment of the present invention, the cathode tab and the cathode
current collector are formed in one piece and the cathode tab may be any one selected
from the group consisting of an aluminum foil, an aluminum mesh, or equivalents thereof.
[0022] FIG. 2A and FIG. 2B are respectively examples of a plan view (2A) and a side sectional
view (2B) illustrating a cathode including a cathode tab which protrudes from a typical
cathode current collector.
[0023] Specifically, as illustrated in FIG. 2A and FIG. 2B, the cathode includes a cathode
active material coating portion 10 on one side or both sides of a cathode current
collector 30, and a cathode tab 20, as a non-coating portion which does not include
the cathode active material coating portion, may be formed at one end of the cathode
current collector 30.
[0024] The cathode tab according to an embodiment of the present invention may be formed
by notching a continuous cathode sheet, in which the one side or both sides of the
cathode current collector are coated with an active material, at a spacing of a unit
electrode using dies.
[0025] According to the present invention, the cathode tab formed after the notching may
be formed as the non-coating portion which does not include the cathode active material
coating portion as illustrated in FIGS. 2A, 2B, 3A and 3B, and may include a portion
of the cathode active material coating portion as illustrated in FIGS. 4 to 6.
[0026] The coating portion of the insulation layer according to an embodiment of the present
invention may be changed according to various factors such as a structure of the battery.
However, the present invention is not limited thereto. Examples of the coating portion
will be described with reference to FIGS. 3 to 6 as follows:
[0027] First, referring to FIG. 3, FIG. 3A and 3B are respectively a plan view (3A) and
a side sectional view (3B) illustrating a cathode including a cathode tab that is
composed of a non-coating portion, according to an embodiment of the present invention.
[0028] Specifically, referring to FIG. 3A and FIG. 3B, the cathode includes a cathode active
material coating portion 10 on one side or both sides of a cathode current collector
30, and a cathode tab 20, which is formed at one end of the cathode current collector
30 as a non-coating portion that does not include the cathode active material coating
portion, may include an insulation layer 40 coated with an insulating material on
one side or both sides thereof.
[0029] According to an embodiment of the present invention, in FIG. 3A, the insulation layer
40 may be coated in an amount of 10% to 90% of a total length (d+ℓ) of the cathode
tab 20 in a protruding direction L of the cathode tab 20, and for example, a length
ℓ of the insulation layer may be in a range of 1 mm to 10 mm. The insulation layer
40 may be coated to have the same width as a width w of the cathode tab 20 which is
perpendicular to the protruding direction L of the cathode tab 20. However, the present
invention is not limited thereto.
[0030] The cathode tab 20 according to another embodiment of the present invention may include
a portion of a cathode active material coating portion 10 as illustrated in FIGS.
4 to 6.
[0031] Referring to FIGS. 4 to 6, the cathode according to an embodiment of the present
invention may include the cathode active material coating portion 10 on one side or
both sides of a cathode current collector 30, and the cathode tab 20 protruding from
the current collector 30 may include a portion of the cathode active material coating
portion 10. The cathode active material coating portion 10 may include an inclined
portion in which the thickness thereof is decreased along a protruding direction of
the cathode tab 20.
[0032] Also, according to an embodiment of the present invention, the cathode active material
coating portion formed on the cathode tab, as illustrated in FIG. 6, may further include
a flat portion between the cathode current collector and the inclined portion, for
example, between the cathode active material coating portion formed on the cathode
current collector and the inclined portion.
[0033] According to an embodiment of the present invention, an insulation layer 40 may be
coated on the cathode tab 20 while including the cathode active material coating portion
10. The cathode active material coating portion 10 formed on the cathode tab 20 may
be a portion of the cathode active material coating portion 10 formed on the cathode
current collector 30 which extends onto the cathode tab 20. Therefore, the cathode
active material coating portion 10 formed on the cathode tab 20 may have the same
material as the cathode active material coating portion 10 formed on the cathode current
collector 30.
[0034] The insulation layer 40 may include a portion (see FIGS. 4 and 6) or all (see FIG.
5) of an inclined surface of the inclined portion of the cathode active material coating
portion 10, and may be formed by being coated in an amount of 10% to 90% of a total
length (d+ℓ) of the cathode tab 20 in the protruding direction of the cathode tab
20. For example, a length ℓ of the insulation layer may be in a range of 1 mm to 10
mm, and the insulation layer 40 may be coated to have the same width as a width of
the cathode tab 20 which is perpendicular to the protruding direction of the cathode
tab 20. However, the present invention is not limited thereto.
[0035] According to an embodiment of the present invention, the insulation layer 40, as
illustrated in FIGS. 4 and 6, may be coated in an amount of 10% to 90% of the total
length (d+ℓ) of the cathode tab in the protruding direction of the cathode tab from
1/2 of an inclined length S of the inclined portion of the cathode active material
coating portion 10 on the cathode tab 20.
[0036] Also, as illustrated in FIG. 5, the insulation layer 40 may be coated in an amount
of 10% to 90% of the total length (d+ℓ) of the cathode tab in the protruding direction
of the cathode tab while including the entire inclined surface (entire inclined length
S) of the inclined portion of the cathode active material coating portion 10 on the
cathode tab 20.
[0037] The insulation layer 40 may be coated to a thickness T of 50% to 100% of a thickness
of the cathode active material coating portion 10 on the cathode tab 20, and for example,
the thickness T of the insulation layer 40 may be in a range of 1 µm to 100 µm. In
the case that the coating thickness T of the insulation layer is excessively thin,
desired electrical insulating properties may be difficult to be obtained. In contrast,
in the case in which the coating thickness T of the insulation layer is excessively
thick, it may be undesirable because solidification time of the coating layer may
increase or an increase in the thickness of the coating layer may be induced.
[0038] According to an embodiment of the present invention, that the insulation layer 40
includes a portion of the cathode active material coating portion 10 is for preventing
the occurrence of a gap, in which the insulation layer is not formed between the cathode
active material coating portion 10 and the cathode tab 20.
[0039] A coating method of the insulation layer that is formed on the one side or both sides
of the cathode tab may also vary. For example, the insulation layer may be formed
by spray coating an aqueous solution including an insulating material on the cathode
tab.
[0040] According to an embodiment of the present invention, the coating of the insulating
material on the cathode tab may be performed in any step of the preparation process
of the secondary battery. However, the present invention is not limited thereto.
[0041] For example, one side or both sides of a cathode current collector are coated with
a cathode active material, and a non-coating portion of the cathode current collector
or a non-coating portion as well as a portion of a cathode active material coating
portion is then coated with an insulating material to form an insulation layer. Then,
a cathode tab including the insulation layer may be obtained by notching the product
thus obtained into a desired shape of the cathode tab using dies.
[0042] As another example of the present invention, a cathode tab is formed by notching
a continuous cathode sheet, in which one side or both sides of a cathode current collector
are coated with a cathode active material, into a desired shape of the cathode tab
at a spacing of a unit electrode using dies, and a cathode tab including an insulation
layer may then be obtained by coating the cathode tab thus formed with an insulating
material.
[0043] Moisture in the cathode coated with the insulating material may be removed by completely
drying the coating layer using a drying method typically known in the art. The drying
may be performed using a hot air method, a direct heating method, and an induction
heating method at a temperature at which moisture is entirely evaporated. However,
the present invention is not limited thereto.
[0044] Also, the present invention may provide a secondary battery including the cathode,
an anode, and a separator disposed between the cathode and the anode.
[0045] FIG. 7 is a schematic view illustrating a secondary battery according to an embodiment
of the present invention. The secondary battery according to the embodiment of the
present invention may include a cathode 100 including a cathode active material coating
portion 10 on a cathode current collector 30; an anode 200 including an anode active
material coating portion 70 on an anode current collector 60; and a separator 300
disposed between the cathode 100 and the anode 200, wherein a cathode tab 20 including
an insulation layer 40, which is coated with an insulating material, extends in the
cathode.
[0046] According to an embodiment of the present invention, a cathode active material used
may be any one selected from the group consisting of lithium-containing transition
metal oxides or equivalents thereof. Specifically, the cathode active material, for
example, may include a manganese-based spinel active material, lithium metal oxide,
or a mixture thereof. Furthermore, the lithium metal oxide may be selected from the
group consisting of lithium-manganese-based oxide, lithium-nickel-manganese-based
oxide, lithium-manganese-cobalt-based oxide, and lithium-nickel-manganese-cobalt-based
oxide, and for example, may include LiCoO
2, LiNiO
2, LiMnO
2, LiMn
2O
4, Li(Ni
aCo
bMn
c)O
2 (where 0<a<1, 0<b<1, 0<c<1, and a+b+c=1), LiNi
1-YCo
YO
2, LiCo
1-YMn
YO
2, LiNi
1-
YMn
YO
2 (where 0≤Y<1), Li(Ni
aCo
bMn
c)O
4 (where 0<a<2, 0<b<2, 0<c<2, and a+b+c=2), LiMn
2-zNi
zO
4, and LiMn
2-zCo
zO
4 (where 0<z<2).
[0047] Also, any one selected from the group consisting of an aluminum foil, an aluminum
mesh, or equivalents thereof may be used as the cathode current collector. However,
the present invention is not limited thereto.
[0048] Copper may be used as the anode current collector according to an embodiment of the
present invention. As an anode active material, a carbon-based anode active material,
such as crystalline carbon, amorphous carbon, or a carbon composite, may be used alone
or in combination of two or more thereof. However, the present invention is not limited
thereto.
[0049] Thicknesses of the cathode and the anode may be in a range of about 10 µm to about
100 µm, and thicknesses of the active materials coated on the current collectors may
be in a range of about 50 µm to about 200 µm. However, the present invention is not
limited thereto.
[0050] According to an embodiment of the present invention, an anode may be prepared to
be larger than a cathode in order to prevent a physical short circuit between the
cathode and the anode.
[0051] Also, a separator may be inserted between the cathode and the anode in order to prevent
a physical short circuit between the cathode and the anode. A porous polymer film,
for example, a porous polymer film prepared from a polyolefin-based polymer, such
as an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer,
an ethylene/hexene copolymer, and an ethylene/methacrylate copolymer, may be used
alone or in a lamination of two or more thereof as the separator. In addition, a typical
porous nonwoven fabric, for example, a nonwoven fabric formed of high melting point
glass fibers or polyethylene terephthalate fibers may be used. However, the separator
is not limited thereto.
[0052] A shape of a battery case accommodating the secondary battery according to the present
invention is not particularly limited, and for example, the battery case may be a
cylindrical type using a can, a prismatic type, or a pouch type. In particular, the
present invention may be used in a prismatic type battery having significant side
effects due to the attachment of an insulating film.
[0053] The cathode tab, on which an insulation layer including an insulating material is
coated according to an embodiment of present invention, may prevent an internal short
circuit which may occur due to cell deformation or sharp edges of electrodes, which
are formed during cutting of the electrodes in a preparation process of the battery,
when the electrodes are stacked, or may prevent a physical short circuit between the
cathode and the anode due to shrinkage of a separator in a high-temperature atmosphere.
Thus, a battery having significantly improved safety and reliability may be prepared,
and furthermore, commercialization of the secondary battery may be facilitated.
<Reference Numerals>
[0054]
- 10:
- CATHODE ACTIVE MATERIAL COATING PORTION
- 20:
- CATHODE TAB
- 30
- CATHODE CURRENT COLLECTOR
- 40:
- INSULATION LAYER
- 100:
- CATHODE 200: ANODE 300: SEPARATOR
- d:
- NON-COATING PORTION
- ℓ:
- LENGTH OF INSULATION LAYER
- w:
- WIDTH OF INSULATION LAYER
- T:
- THICKNESS OF INSULATION LAYER
INDUSTRIAL APPLICABILITY
[0055] Since an insulation layer formed of an insulating material is included on a cathode
tab, the present invention may reduce the possibility of a physical short circuit
between a cathode and an anode due to cell deformation or shrinkage of a separator
in a high-temperature atmosphere. In addition, safety and reliability in battery performance
may be significantly improved.
1. A cathode comprising:
a cathode current collector;
a cathode tab protruding from the cathode current collector; and
an insulation layer coated with an insulating material on the cathode tab.
2. The cathode of claim 1, wherein the insulating material comprises any one selected
from the group consisting of butyl acrylate, styrene, acrylic acid, hydroxyethyl acrylate,
and a styrene-butadiene rubber (SBR), or a mixture of two or more thereof.
3. The cathode of claim 1, wherein the insulating material is an aqueous solution in
which the insulating material is dispersed in an amount of 10 wt% to 90 wt% in water.
4. The cathode of claim 1, wherein the cathode tab is a non-coating portion which does
not include a cathode active material coating portion.
5. The cathode of claim 4, wherein the insulation layer is coated in an amount of 10%
to 90% of a total length of the cathode tab in a protruding direction of the cathode
tab.
6. The cathode of claim 4, wherein the insulation layer is coated to have a same width
as a width of the cathode tab which is perpendicular to the protruding direction of
the cathode tab.
7. The cathode of claim 1, wherein the cathode tab comprises a portion of a cathode active
material coating portion.
8. The cathode of claim 7, wherein the cathode active material coating portion comprises
an inclined portion in which a thickness thereof is decreased along a protruding direction
of the cathode tab.
9. The cathode of claim 8, wherein the insulation layer comprises a portion or all of
an inclined surface of the inclined portion and is coated in an amount of 10% to 90%
of a total length of the cathode tab in the protruding direction of the cathode tab.
10. The cathode of claim 8, wherein the insulation layer is coated in an amount of 10%
to 90% of a total length of the cathode tab in the protruding direction of the cathode
tab from 1/2 of an inclined length of the inclined portion.
11. The cathode of claim 8, wherein the cathode active material coating portion further
comprises a flat portion between the cathode current collector and the inclined portion.
12. The cathode of claim 7, wherein the insulation layer is coated to a thickness of 50%
to 100% of a thickness of the cathode active material coating portion on the cathode
tab.
13. The cathode of claim 1, wherein a length of the insulation layer is in a range of
1 mm to 10 mm.
14. The cathode of claim 1, wherein a thickness of the insulation layer is in a range
of 1 µm to 100 µm.
15. The cathode of claim 1, wherein the insulation layer is coated on the cathode tab
by spray coating.
16. A secondary battery comprising:
the cathode of claim 1;
an anode; and
a separator disposed between the cathode and the anode.
17. The secondary battery of claim 16, wherein the anode is larger than the cathode.
18. The secondary battery of claim 16, wherein the secondary battery is a cylindrical,
prismatic, or pouch type battery.